1. Field of the Invention
The present invention relates to a connection structure between both circuit boards and a connection method for connecting both the circuit boards.
2. Description of Related Art
For connecting both circuit boards, there is a tendency to adopt a connection structure in which plural connection terminals are arranged on each of the circuit boards, and the circuit boards are disposed so that these connection terminals are overlapped with each other to be connected by soldering or the like. When an electronic product package is used in practice, the whole circuit board is sometimes exposed to low-temperature and high-temperature environment (for example, xe2x88x9240xc2x0 C. to 150xc2x0 C.) in repetition. In this case, the temperature of the terminal connection portion is changed between a low temperature and a high temperature, thereby causing heat strain at the terminal connection portion. Due to occurrence of this heat strain in repetition in the terminal connection portion, the terminal connection portion may be ruptured.
When a large current is supplied to the connection portion, it is advantageous to enlarge each connection terminal as much as possible. However, when the size of the connection terminal is made larger, an arrangement pitch of the connection terminals becomes wider. In this case, the above-described heat strain further becomes larger, and a period from the occurrence of fatigue to the rupture becomes shorter.
In view of the foregoing problems, it is an object of the present invention to provide a connection structure of both first and second circuit boards, which reduces heat strain in the circuit boards, and improves fatigue life of a connection portion of both the circuit boards.
It is an another object of the present invention to provide a connection method for connecting both first and second circuit boards while reducing the heat strain in the circuit boards and improving the fatigue life of the connection portion.
According to the present invention, in a connection structure for both first and second circuit boards, a plurality of first connection terminals are arranged on the first circuit board in an arrangement direction, a plurality of second connection terminals are arranged on the second circuit board in the arrangement direction, and an electrical conductive material is disposed between the first and second connection terminals. The first connection terminals and the second connection terminals are disposed opposite to each other, to be overlapped with each other. Further, the first and second circuit boards are disposed to be connected to each other by connecting the first and second connection terminals using the electrical conductive material, the first and second connection terminals are arranged to have a first arrangement pitch in a predetermined range from a center in the arrangement direction and to have a second arrangement pitch at an endmost portion or/and in a vicinity of the endmost portion, and the second arrangement pitch is smaller than the first arrangement pitch. Accordingly, in the connection structure, heat strain applied to the connection terminals at the endmost portion and in the vicinity of the endmost portion can be made smaller, and the fatigue life in the connection portion of both the first and second circuit boards can be improved.
According to the present invention, a connection method for connecting first and second circuit boards includes, forming a plurality of first connection terminals to be arranged on the first circuit board in an arrangement direction, forming a plurality of second connection terminals to be arranged on the second circuit board in the arrangement direction, disposing the first connection terminals and the second connection terminals opposite to each other to be overlapped to each other, and connecting the first connection terminals and the second connection terminals by using an electrical conductive material. In the connection method, the first and second connection terminals are arranged in the first and second circuit boards to have a first arrangement pitch in a predetermined range from a center in the arrangement direction and to have a second arrangement pitch at an endmost portion or/and in a vicinity of the endmost portion, and the second arrangement pitch is smaller than the first arrangement pitch. Accordingly, in this connection method, the first and second circuit boards can be readily connected while reducing the heat strain in the circuit boards and improving the fatigue life of the connection portion.